Neutralino

In elementary particle physics are neutralinos hypothetical elementary particles that occur in supersymmetric theories. These are characterized by the fact that any ( quantum ) field field is assigned a partner, which differs in spin from the original by the amount of 1/2. Since the output fields here are bosons ( integer spin), the neutralino fermions themselves must therefore be ( half-integer spin). In particular, the neutralino Majorana fermions, ie they have no electrical charge and therefore do not differ from their antiparticles.

Four neutralinos in the MSSM

Neutralinos are superposition states ( mixtures, linear combinations ) of super partners both electrically neutral in color calibration and Higgs fields. In the former, it is the gauginos ( Wino, partner of W0 ) and ( Bino, partner of B0), the latter to the Higgsinos and (partner of the hypothetical Higgs bosons and ).

A direct identification of a neutralino with a partner of a field calibration or Higgs field is generally not possible, as these usually do not have a defined mass. Typically, existing in a model neutralinos are named in ascending order according to their mass. In the minimal supersymmetric standard model ( MSSM ), these are neutralino 1-4, abbreviated as (sometimes ).

Alternative composition

The postulated neutralino can also as a superposition of photino and Zino uncharged constructs (instead of Wino and Bino ) can be expressed with the uncharged Higgsinos.

Photino and Zino are in fact linear combinations of themselves already and that should be taken in the same way as in the Standard Model photon and Z0 boson, the electrically neutral gauge bosons of the electroweak interaction, from the neutral gauge fields W and B0:

Here is the Weinberg angle and the wave function.

Because of the unrecognized mixture of fields and with the uncharged Higgsinos are photino and Zino generally not candidates for observable particles.

Scenarios for the two light neutralino

Moortgat -Pick and Fraas have been investigated for the two lighter neutralinos and three different scenarios. It will be differentiated strengths of the shares photino, Zino and Higgsinos and to the mixture, whereby different identifications of the two neutralinos suggested by individual units or even impossible:

The lightest neutralino as a WIMP candidate

Of particular importance is the lightest neutralino. In many models, it is stable, has a mass of a few hundred GeV / c ² ( proton mass for comparison: 0.94 GeV / c ²) and due to its lack of electric charge a low interaction with light. Therefore, it would, as the lightest supersymmetric particle (LSP ) is a promising candidate for dark matter, a so-called WIMP. The Particle Data Group announced in 2006 as an experimental lower limit on the neutralino mass 46 GeV / c ² to.